1. Field of the Invention
This invention relates to a magnetic powder and a magnetic recording medium using the magnetic powder.
2. Description of the Prior Art
A magnetic recording medium of the type which is produced by the application of a coat is composed of a supporting substrate made of a nonmagnetic such as polyethylene terephthalate and a magnetic layer formed mainly of a magnetic powder and a binder resin and superposed on the supporting substrate.
The magnetic powders heretofore used for magnetic recording media include needle like magnetic powders such as of .gamma.--Fe.sub.2 O.sub.3, Co-coated .gamma.--FeO.sub.3, Co-doped .gamma.--Fe.sub.2 O.sub.3, Co-coated Fe.sub.3 O.sub.3, and metallic Fe, for example. For the magnetic recording media using these needle like magnetic powders, the longitudinal magnetic recording method utilizing the magnetization which is effected in the longitudinal direction relative to the surface of a magnetic layer has been adopted.
This longitudinal magnetic recording method, however, has proved unfit for high-density recording and reproducing because the effect of a demagnetized field becomes more conspicuous in proportion as the recording density increases.
In recent years, therefore, the perpendicular magnetic recording method utilizing the magnetization which is effected in the perpendicular direction relative to the surface of a magnetic layer has been proposed. This perpendicular magnetic recording method may well be regarded as optimal for high-density recording because this magnetization gains stability as the recording density increases exalts.
As magnetic recording media fit for this perpendicular magnetic recording method increases magnetic recording media which are obtained by depositing a Co--Cr alloy on a supporting substrate, for example, by a vacuum technique such as the vacuum deposition method or the sputtering method and the magnetic recording media which are obtained by applying a hexagonal system ferrite powder having an axis of easy magnetization in a direction perpendicular to a surface together with a binder resin to a supporting substrate have been known.
The magnetic recording media which are produced by the vacuum technique have various problems pertaining to ability to withstand weather conditions, capability of mass production, and production cost, whereas the magnetic recording media which are produced by the coating technique have great promise of success and are attracting attention because they allow ready use of conventional manufacturing facilities and, what is more, excel in capability of mass production.
As specific examples of the hexagonal system ferrite powder which is used for the magnetic recording media of the coating type, M type BaFe.sub.12 O.sub.19, W type BaMe.sub.2 Fe.sub.16 O.sub.27 (wherein Me stands for a divalent metal element), hexagonal system ferrite powders resulting from substitution of part of the atoms by atoms of other elements, M type and W type composite powders, and M type and Spinel composite powders may be cited.
For the production of these magnetic powders, various methods including the glass crystallization method, the hydrothermal synthetic method, the coprecipitation method, and the flux method have been proposed.
For allowing a large volume of information to be recorded and reproduced, the magnetic recording media are desired to be capable of recording the information at a still higher density. With a view to realizing such a magnetic recording medium, the desirability of developing a method which allows high packing of magnetic powder and consequently enjoys increases output and diminished noise has been finding growing recognition.
None of the magnetic powders developed to date, however, is capable of attaining the high packing and further fulfilling the diminution of noise.